£1k trading allowance

Hello I made c.£1050.00 in ad hoc self employment. I understand I have a trading limit £1000.00. I completed a self assessment and I need to pay tax of approx £350 - I would have thought it would have been just for the amount over the trading allowance no? When I was completing my self assessment should I have only put £50 turnover so to minus the trading allowance. If it’s correct it doesn’t seem fair, so I’m leaning on thinking there’s an error somewhere.

Hi,
As we would need to access your record to check the calculation you will need to contact our Self Assessment team.
Self Assessment: general enquiries
Thank you.